Thermo-switch for fire alarm systems



June 28, 1955 T. BRONEE THERMO-SWITCH FOR FIRE ALARM SYSTEMS Filed June 4, 1951 I N VE NTOR m m O www w L f B W7 W e 1n WMM T m nited States Patent O 'lHERMO-SWIT CH FOR FIRE ALARM SYSTEMS Torben Brone, Copenhagen, Denmark Application June 4, 1951, Serial No. 229,661

Claims priority, application Denmark June 6, 1950 4 Claims. (Cl. 200-138) This invention relates to a thermoswitch for fire alarm systems, and more particularly a thermoswitch of the general type disclosed in the copending application Ser. No. 794,229 to Hans Christian Hansen, filed on December 29, 1947, now Patent No. 2,556,582 issued June 12, 1951.

Broadly, this type of switch comprises bimetallic means and switching means operable in response to temperature variations of said bimetallic means. By preference provision is made for both primary and secondary bimetallic means in different heat exchange relationship to the surroundings, the arrangement being such that said switching means is operable in response to temperature diierences between said primary and secondary bimetallic means, and consequently in response to the rate of temperature variations of the surroundings.

In the said patent there is disclosed a special mounting of the primary and secondary bimetallic means in com bination with a magnetic snap action type switching member whereby a high degree of mechanical balance as well as a minimum ot frictional resistance to operation has been achieved so that a very reliable function of the switch in response to temperature variations of the surroundings can be expected in the majority of cases.

However, if thermoswitches of the type described are used under conditions where they are very much subjected to moisture or to atmospheric inuences of particularly injurious nature, such as on board of ships, the metal parts of the thermoswitch and particularly the mov able part may in the course of time be attacked or corroded so much that the thermoswitch is not ready for operation if and when a tire eventually occurs. Also, if ire alarm switches are used under conditions where they are strongly subjected to vibrations, such as on board of ships, there is a danger that the switch may be operated improperly as a consequence of such vibrations.

One object of the invention is to devise a thermoswitch for tirel alarm systems in which the danger of failure to operate as a consequence of corrosion caused by the'surrounding atmosphere as well as the danger of improper operation on account of vibrations are considerably reduced or substantially eliminated.

`Another object of the invention is to construct a thermoswitch in which the movable parts are enabled to work in an oil bath without for that reason substantially reducing the accessiblity of the vital parts of the switch for inspection and repair.

A further object of the invention is to provide means whereby the vital parts of a thermoswitch of the character referred to may be effectively protected against the surrounding atmosphere without substantially reducing the sensibility of the switch to temperature variations of the surrounding atmosphere.

With these and other objects in view, according to one feature of the invention, a thermoswitch for tire alarm systems comprises, in combination, a socket, an elongated casing projecting from said socket, bimetallic means mounted in lateral recesses of said socket, switching means in said casing operable in response to temperature fice variations of said bimetallic means, and a sheath closed at one end and slidable along and fitting snugly around said casing.

Other features of the invention will appear from the following detailed description of one embodiment, reference being had to the accompanying drawings in which:

Fig. l shows a thermoswitch constructed in accordance with the invention, as viewed in side elevation with section through a sheath belonging to the switch,

Fig. 2 one part of a bipartite casing forming part of the construction of Fig. 1, and

Fig. 3 a perspective view of the sheath of the switch.

1n the drawing, 1 is a socket adapted to be attached to a ceiling or the like horizontal support in a room to be protected by means of a tire alarm system. The socket 1 may comprise terminals for connecting the various conductors, not shown, forming part of the electric circuit in which the thermoswitch is intended to be interposed.

Reference character 2 indicates generally a casing attached to and projecting downwards from the socket 1 and serving to accommodate the operating parts of the thermoswitch. The casing 2 is composed of two parts, one of which, 3, is shown separately in Fig. 2, the other part of the casing being exactly similar so that the two parts may be closed together to form a closed casing.

The casing part 3 has a top wall 4, a bottom wall 5, a back wall 6 and two side walls 7 and 8. The two side walls are cut away at the top to leave lateral recesses in the casing, and in the same zone the back wall 6 is cut back to form a relatively narrow strip 9, along the edges of which there are arranged two partitions 10 and 11 parallel to the side walls 7 and 8. lt will be understood that when the two casing parts are closed together, the partitions 10 and 11 will combine with the similar partitions of the other casing part to form a narrow closed compartment 12 located between two lateral recesses 13 and 14 of the casing, while below the said narrow compartment and recesses another compartment is formed between the side walls 7 and 8 and the bottom wall 5 of the casing.

Attached to the upper end of each of the side walls 7 and 8 is the outer end of a bimetallic spiral 15 and 16, respectively, mounted in a position such as to have its outer face as nearly as possible ush with the outer face of the respective side wall. In practice, the spiral should of course be located at some distance from the extended plane of the outer face of the Wall 7 or 8, but the spiral should be mounted in a positon such that it comes as close as possible to the said plane without interfering with the sheath to be mentioned below. Carried between the inner ends of the two spirals 15 and 16 is a spindle 17 extending oatingly through the narrow compartment 12 and having a third bimetallic spiral 18 mounted'thereon within the said compartment. The outer end of the spiral 18 is bent to form a tongue 19 serving to operate a switching lever 20 carried by coil springs 21 and 22 between two lugs 23, 24 projecting from the side walls 7 and 8. The switching lever 20 has one end located in the path of movement of the tongue 19 while its other end is arranged for co-operation with a permanent magnet 25 serving to move the switching lever at snap action when operated by the tongue 19. 26 and 27 are two resilent tongues mounted in the casing in a manner such as to be biased against two contact pieces 28 and 29 likewise mounted in the casing. Mounted on the free ends of the resilient tongues 26 and 27 is an insulating cross piece 30 lying in the path of movement of the switching lever 20 so that when the latter is operated and then attracted by the permanent magnet 2S, it will strike the cross piece 30 and thereby disengage the resilient tongues 26 and 27 from the contact pieces 28 and 29.

31 is a sheath constructed to fit snugly around the circumference of the casing and adopted to be readily slid on to the casing and withdrawn therefrom. Before sliding the sheath on to the casing, a certain quantity of oil may be filled into the sheath so that the oil will substantially fill the lower compartment of the casing in which the switching lever and contact means are arranged. The total length of the sheath is such that it will cover the casing in the whole of its length and will thus also cover the recesses 13 and 14 in which the bir'netallic spirals 15 and 16 are arranged. The sheath 31 has a relatively small wall thickness and is made from heat conductive material so as to permit a rapid heat exchange therethrough. In order to increase the rate of heat exchange between the sheath and the surrounding atmosphere the sheath may preferably be provided at its top with radially projecting ribs 32, which may be braced at their free ends by means of a ring 33.

It will be understood that the sheath offers a very good protection of all active parts of the thermoswitch. If oil is filled into the sheath, which is preferably but not necessarily the case, such parts of the thermoswitch as dip into the oil will be directly protected thereby, and the parts located above the oil level will also be protected by the oil vapour present above the oil level. Preferably the oil level should be selected below the bimetallic spirals 15 and 16 in order not to reduce the transmission of heat from the sheath to the bimetallic spirals. Be-

sides protecting the active parts of the thermoswitch against atmospheric influences, the oil in the sheath also offers a good protection against improper switching operations as a consequence of vibrations `by offering a considerable resistance to vibratory movements of the switching lever.

Notwithstanding the good protection offered by the sheath, the latter does not substantially interfere with the accessibility of the thermoswitch for inspection, because all that is necessary is to slide the sheath olf the casing in order to get full access to the thermoswitch proper.

It will be understood that since the outer or primary bimetallic spirals are located very close to the sheath, and since the latter, on account of its small wall thickness and the heat conduction nature of the material of which it is made, offers a high rate of heat transmission, the outer spirals will respond quickly to temperature variations of the surrounding atmosphere. On the other hand, the inner or secondary bimetallic spiral is located in an insulated compartment and will therefore only be heated with considerable delay. Accordingly, since the position of the tongue 19 of the secondary bimetallic spiral depends on the temperature difference between the primary and secondary bimetallic spirals, this tongue, in the case of a rise of the temperature of the surroundings, will be moved in dependence of the rate at which the temperature of the surroundings increases. Thus, it will be seen that the provision of the sheath Vdoes not interfere with the so-called differential principle on which the active parts of the switch are built up.

It will be understood that many modifications may be made of the specific arrangements shown without exceeding the scope of the invention and that particularly the detailed construction of the active parts of the thermoswitch is by no means essential to the principles of the invention.

I claim:

l. A thermoswitch comprising a top socket, an elongated casing projecting downwards from said socket and having lateral recesses therein provided at the top end of said casing, bimetallic means mounted in the lateral recesses of said casing in positions substantially flush with the outer wall of said casing, switching means in said casing operable in response to temperature variations of said bimetallic means, and an oil receiving sheath of heat conductive material closed at its bottom end, said sheath fitting snugly around said casing and being slidable therealong to a position in which it covers said recesses and said sheath having a supply of oil therein at a level just below the bimetallic means and said sheath having a length substantially equal to the total length of said casing, said bimetallic means being provided very close to the walls of the sheath.

2. A thermoswitch according to claim l, in which said sheath is provided with radially projecting heat conducting ribs at its top end.

`3. AA thermoswitch comprising a top socket, an elongated casing projecting downwards from said socket, said casing having recesses on two opposite sides thereof and being shaped to form a heat insulating compartment between said recesses, said recesses being provided at the top end of said casing, primary bimetallic means mounted in said recesses in positions substantially flush with the outer wall of said casing, secondary bimetallic means mounted in said heat insulating compartment, switching means in said casing operable in response to temperature difference between said primary and secondary bimetallic means, and an oil receiving sheath of heat conductive material closed at its bottom end, said sheath fitting snugly around said casing and being slidable therealong to a position in which it covers said recesses and said sheath having a supply of oil therein at a level just below the bimetallic means and said sheath having a length substantially equal to the total length of said casing, said primary bimetallic means being provided very close to the walls of the sheath.

4. A thermoswitch according to claim 3, in which said sheath is provided with radially projecting heat conducting ribs at its top end.

References Cited in the file of this patent UNITED STATES PATENTS 1,246,792 Schweitzer et al Nov. 13, 1917 1,605,057 Nichols Nov. 2, 1926 1,931,238 Phelan Oct. 17, 1933 1,990,219 Baird Feb. 5, 1935 2,113,296 Durbin Apr. 5, 1938 2,389,592 Bucklen et al Nov. 27, 1945 2,431,945 Little et al a Dec. 2, 1947 2,556,582 Hansen June 12, 1951 

1. A THERMOSWITCH COMPRISING A TOP SOCKET, AN ELONGATED CASING PROJECTING DOWNWARDS FROM SAID SOCKET AND HAVING LATERAL RECESSES THEREIN PROVIDED AT THE TOP END OF SAID CASING, BIMETALLIC MEANS MOUNTED IN THE LATERAL RECESSES OF SAID CASING IN POSITIONS SUBSTANTIALLY FLUSH WITH THE OUTER WALL OF SAID CASING, SWITCHING MEANS IN SAID CASING OPERABLE IN RESPONSE TO TEMPERATURE VARIATIONS OF SAID BIMETALLIC MEANS, AND AN OIL RECEIVING SHEATH OF HEAT CONDUCTIVE MATERIAL CLOSED AT ITS BOTTOM END, SAID SHEATH FITTING SNUGLY AROUND SAID CASING AND BEING SLIDABLE THEREALONG TO A POSITION IN WHICH IT COVERS SAID RECESSES AND SAID SHEATH HAVING A SUPPLY OF OIL THEREIN AT A LEVEL JUST BELOW THE BIMETALLIC MEANS AND SAID SHEATH HAVING A LENGTH SUBSTANTIALLY EQUAL TO THE TOTAL LENGTH OF SAID CASING SAID BIMETALLIC MEANS BEING PROVIDED VERY CLOSE TO THE WALLS OF THE SHEATH. 